The invention relates to an intravascular catheter which finds particular advantage in the form of a microcatheter, which is capable of penetration deeply into the branching small arteries of the heart, the brain, the liver, or other organs of the body for the application of chemotherapy or x-ray visualization of the blood vessel structure.
Brain catheters are also used for the infusion of embolic coils in aneurysms and infusion of embolic agents in arterio-venous malformations and fistulas (vessel ruptures). An example of an embolic agent or sealing agent is cyanoacrylate which embolizes or seals the required vessel. This is usually done only in the smaller branch arteries, so that a catheter used to provide such materials must have a highly flexible tip coupled with good pushability, all in conjunction with a small outside diameter. Typically, such microcatheters may have a width of no more than about 0.05 inch, or no more than substantially three French size.
In the prior art, efforts have been made to provide thin catheters which have distal ends that are more flexible than a proximal portion of the catheter. For example, Engelson U.S. Pat. No. 4,739,768 and its reexamination certificate disclose such a catheter. Sepetka U.S. Pat. No. 4,955,862 discloses a catheter having a thinner distal end which carries a helical reinforcing spring. See also Castaneda et al. U.S. Pat. No. 5,279,596.
By this invention, an intravascular catheter which is preferably of French three size or less is provided, which catheter is particularly capable of advancement into small arteries, having a stepwise gradient of increasing flexibility along the catheter extending from a proximal portion toward the distal end. The catheter is capable of advancement and deep penetration into brain arteries for example, so that a therapeutic agent may be delivered to a precise location deep inside the brain, which location would be inaccessible to many other catheters.